Electric machines employed in commercial and industrial applications are often required to operate at 100% of the applicable power rating over what is typically a 60,000-hour service life. Therefore, a motor or other electric machine employed in a commercial or industrial setting must be both reliable and versatile. Machine reliability and lifespan can be compromised by many factors including but not limited to: 1) high temperature operation resulting in thermally induced component failures, 2) vibration, heat, friction, unbalanced operation, contamination, inadequate material selection or other causes of mechanically induced component failure, or 3) dielectric failure resulting in electrical short circuits or open circuits caused by heat, inadequate material selection or other causes.
Electric machines are often provided with a mechanical cooling system, for example a fan plus a cowling configured to direct air over cooling fins cast into the machine housing. Many such devices are classified as totally enclosed fan cooled (TEFC) devices. TEFC motors suffer from inherent inefficiency since a portion of the total power output by the motor must turn the cooling fan, and therefore is unavailable for output. For example, a TEFC motor attached to a conveyor belt must operate both the cooling fan and the conveyor belt, therefore the portion of the motor output required to turn the fan is not available at the conveyor belt. The fan and cowling apparatus of a TEFC machine is prone to damage, and presents a safety risk in a typical industrial setting. Furthermore, since a TEFC machine drives a cooling fan with one side of the motor shaft, it is impossible or difficult to attach two downstream machines to a single TEFC motor.
Conventional electric machines are made robust and durable usually by implementing the machines with large and heavy components. The larger and heavier components required to promote stable long-term operation can increase machine cost and weight.
Other electric machines, having directly ventilated and therefore partially open housings to promote cooling, can suffer from moisture and particulate matter contamination which in turn can cause mechanical component degradation and wire insulation or electric junction degradation and premature failure. Totally enclosed nonventilated (TENV) electric machines present unique cooling challenges since TENV devices lack direct ventilation or an external fan moving air over external cooling fins.
The embodiments disclosed herein are designed to minimize one or more of the above problems.